96. We turn tonight to the philippines. What are some tourists looking for? Abc's alex marquardt was there, as cameras rolled and a big bust went down. Reporter: We traveled to the picturesque subic bay in the western philippines, a hotspot for sex tourism. The american ambassador recently estimated that 40% of american men here come for sex. To investigate the rampant underage prostitution, producer alex waterfield and I go undercover with hidden cameras. We'd been told about this man, arthur benjamin, a 49-year-old texan who has lived here for 25 years. He's suspected of pimping out underage girls from his bar. Over coffee, he tells us about how he melt his 16-year-old girlfriend. Needed somebody to take care of her. Come here. You know what I want. Reporter: And how, with the help of his bar manager, lucy, underage girls have worked in his bar. One of them is 16-year-old princess, who has given us permission to show her face. Little did benjamin know, filipino and american authorities were planning a raid on his bar. That's it. Go, go, get out, go! Reporter: Benjamin is stunned. That's when we reveal ourselves to him. We're with abc news. You told us that you have had underage sex with multiple girls and underage girls have worked in this bar. I have never had underage girls here and I do not have sex with underage girls. Reporter: Then, we tell him we have it on hidden camera. Does that change anything that you told me? Nope. Reporter: Benjamin was arrested. Tonight, he is in jail awaiting charges. Activists say authorities aren't doing nearly enough, but every arrest is a blow against a dark world. Alex marquardt, abc news, subic bay.

This transcript has been automatically generated and may not be 100% accurate.

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